The present invention relates to a magnetron oscillating apparatus and, more particularly, to a magnetron oscillating apparatus which oscillates a microwave by applying a voltage between the cathode and the grounded anode of the magnetron.
In manufacturing semiconductor integrated circuits, plasma processing apparatuses are used, which execute processes such as crystal growth, etching, and ashing by the effect of plasma produced by a microwave. In plasma processing apparatuses of this type, a magnetron is often used as a microwave oscillator.
A magnetron forms an electric field between the cathode and the anode and oscillates a microwave by the interaction between electrons emitted from the cathode toward the anode and a magnetic field applied in the direction perpendicular to the electric field. The magnetron is inexpensive and efficient for it.
FIG. 8 shows the arrangement of a conventional magnetron oscillating apparatus. Referring to FIG. 8, a magnetron 1 has a heater/cathode H/K in which a cathode and a heater are integrated, and an anode A. The anode A composed of a plurality of vanes and is provided concentrically with respect to the cathode K. A resonator is formed by spaces partitioned by the vanes.
The heater power supply 3 is connected to the two terminals of the heater/cathode H/K. When the heater power supply 3 supplies a current to the heater/cathode H/K, the heater/cathode H/K is heated and emits electrons.
The anode power supply 2 serving as a power supply unit is connected to one terminal of the heater/cathode H/K. When a negative voltage with respect to the anode A connected to ground is applied from the anode power supply 2 to the heater/cathode H/K, an electric field is formed between the heater/cathode H/K and the anode A. The heater/cathode H/K emits electrons toward the anode A.
The low-pass filter composed of coils L1 and L2 and capacitors C1 and C2 is provided between the heater/cathode H/K and the power supplies 2 and 3 to prevent energy of the microwave generated by the magnetron 1 from flowing into the anode power supply 2 and heater power supply 3. The coils L1 and L2 are connected between the two terminals of the heater/cathode H/K and the capacitors C1 and C2. Feed through capacitors inserted in through holes for formed at the case are used as capacitor C1 and C2 to connect from the heater/cathode H/K to the outside. The capacitors C1 and C2 correspond to capacitors which are connected between ground and the connection points between the coils L1 and L2 and the heater power supply 3.
In the above-described conventional magnetron oscillating apparatus, a voltage is applied from the anode power supply 2 to make the magnetron 1 oscillate. When plasma is produced by a microwave power obtained in this way, high-density plasma can be obtained at a low pressure. This plasma also has an electron temperature lower than plasma produced by a high-frequency which has a frequency lower than the microwave.
However, in a plasma processing apparatus including the conventional magnetron oscillating apparatus, for example, when etching is executed to form a fine contact hole in a silicon oxide film, the selectivity for underlying silicon decreases. Additionally, abnormal side etching or dielectric breakdown occurs due to accumulated charges in etching a gate polysilicon electrode. For this reason, micropatterning for a line width of 1 μm or less is difficult.